Time Evolution of the Electronegativity - Modern Trends in Chemistry and Chemical Engineering - page 17

Boyd and Edgecombe [94] expressed the electronegativity of atom A as a power
curve of F A

χ A = aF b (61)

The two constants or parameters are computed as a = 1.938 and b = -0.2502 to
provide the electronegativities of Li and F as 1.00 and 4.00 respectively and then Boyd
and Edgecombe [94] evaluated the atomic electronegativity of the 21 elements of the
second, third and fourth periods using the computed “a” and “b” values and the taking
the electronegativities data of Li and F as references.

Allen's Scale of Electronegativity [13]
Perhaps the simplest definition of electronegativity is that of Allen [13] who stated that
electronegativity is the average energy of the valence electrons in a free atom.
Allen proposed the electronegativity ansatz as:

χ Allen = (n s ε s + n p ε p )/(n s + n p ) (62)

where ε s and ε p are the one-electron energies of s- and p-electrons in the free atom
and n s and , n p are the number of s- and p-electrons in the valence shell respectively.
It is usual to apply a scaling factor, 1.75 × 10 −3 for energies expressed in kilojoules
per mole or 0.169 for energies measured in electron volts, to give values which are
numerically similar to Pauling electronegativities.
Furthermore, Allen [13, 14] considered electronegativity as confi guration energy
of the atoms of interest and he stated that “when orbital occupancy is taken into ac-
count, it immediately follows that confi guration energy (CE), the average one-electron
valence shell energy of a ground-state free atom, is the missing third dimension.”
For s-p block elements, the Allen's Scale of electronegativity is

χ s-p = (CE) s-p = (n s ε s + n p ε p )/( n s + n p ) (63)

and for the atoms with ground-state confi gurations s n d m and s n-1 d m+1 , the Allen's
Scale of electronegativity is

χ d = (CE) d = (pε s + qε d )/( p + q) (64)

where ε s and ε d are the multipulate-averaged one-electron energies of s- and d-
orbitals of the atom in the lowest energy confi guration respectively. In the free atom n
and m are the usual integers such that (p + q) is the maximum oxidation state observed
for the atom in any compound or complex ion.
The multipulate-averaged one-electron energies can be directly determined from
spectroscopic data, and so the electronegativities calculated by this method are origi-
nally referred to as spectroscopic electronegativities by Allen. The credit of the scale
is that the necessary data to compute the electronegativities of atoms are available for
almost all elements, and hence, this method allows us to compute the electronegativi-
ties of the elements which cannot be evaluated by other methods. However, for d- and
f-block elements, doubt in the electronic confi guration may arise for the calculation of
the electronegativity by Allen's method.